Recent activity

The geomagnetic field was quiet on April 13. Solar wind
speed ranged between 406 and 461 km/sec.

Solar flux measured at 20h UTC on 2.8 GHz was 93.1. The planetary A
index was 6 (STAR Ap - based on the mean of three hour interval ap indices: 7.5).
Three hour interval K indices: 22222222 (planetary), 22223221 (Boulder).

The background x-ray flux is at the class A8 level.

At midnight there were 5 spotted regions on the visible disk. The solar flare activity level was very low. No C class
events were recorded during the day.

Region 10588 decayed slowly and will rotate over the southwest limb today.
Region 10591 decayed further and could soon become spotless.
New region 10592 emerged near the southeast limb on April 12 and was numbered by SEC the next day.

Spotted regions not numbered by NOAA/SEC:
[S387] A new region emerged quickly in the southeast quadrant just east of region 10591 on April 12. Moderately quick
development was observed on April 13. There is not much
separating the leading negative polarity field of this region from the trailing positive polarity area of region 10591. Location at midnight:
S16W12.
[S390] This region rotated partly into view at the northeast limb on April 13. Location at midnight: N14E83.

Coronal mass ejections (CMEs)

April 12-13: No fully or partly Earth directed CME observed.April 11: A fast, full halo CME was observed after a C9 event in region S380 early in the day. This CME is likely to impact Earth on April
14. Another full halo CME was observed near noon, its source was probably a few days behind the northwest limb.

Coronal holes

A very small coronal hole (CH89) in the southern hemisphere was in a possibly geoeffective position on April 12 and could cause a weak
geomagnetic disturbance on April 15. A poorly defined coronal hole (CH90) in the northern hemisphere could be in a
geoeffective position on April 13-14.

Processed SOHO/EIT 284 image at 19:05 UTC on April 13. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet early on April 14. A likely CME impact during the first half of
the day could cause active interval. Quiet to unsettled is likely on
April 15 while a weak high speed stream from coronal hole CH90 could arrive on April 16 and cause some unsettled and active
intervals that day and on April 17.

Long distance low and medium frequency (below 2 MHz) propagation along
east-west paths over high and upper middle latitudes is poor to fair. Propagation along long distance north-south paths is poor to
fair. [Trans
Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del
Uruguay before 02h UTC, then Radio Vibración (Venezuela) with a fairly strong signal. 590 VOCM and CJYQ on 930 kHz had good
signals].

Coronal holes (1)

Coronal mass ejections (2)

M and X class flares (3)

1) Effects from a coronal hole could reach Earth within the next 5 days. When the high speed stream has arrived
the color changes to green.
2) Material from a CME is likely to impact Earth within 96 hours.
3) There is a possibility of either M or X class flares within the next 48 hours.

Data for all numbered solar regions according to the Solar Region Summary provided by
NOAA/SEC. Comments are my own, as is the
STAR spot count (spots observed at or inside a few hours before midnight) and data for regions not numbered by SEC or where SEC has observed no spots.
SEC active region numbers in the table below and in the active region map above are the historic
SEC/USAF numbers.

Active region

Date numbered

SEC
spot
count

STAR
spot
count

Location at midnight

Area

Classification

Comment

10588

2004.04.01

1

1

S13W80

0060

HSX

area was 0050
at midnight,

10589

2004.04.05

N11W49

plage

10591

2004.04.12

9

5

S16W13

0050

CAO

location was S15W16
at midnight, area 0020,
classification CRO

10592

2004.04.13

1

1

S12E59

0020

HSX

formerly region S389

S380

emerged on
2004.04.03

S17W78

plage

S383

emerged on
2004.04.05

S19W72

plage

S385

emerged on
2004.04.11

S17W56

plage

S387

emerged on
2004.04.12

16

S16W12

0110

DAI

S388

emerged on
2004.04.12

S07E42

plage

S390

visible on
2004.04.13

2

N14E83

0040

CSO

Total spot count:

11

25

SSN:

41

75

Monthly solar cycle data

Month

Average solar
flux at Earth

International sunspot number

Smoothed sunspot number

2000.04

184.2

125.5

120.8
cycle 23 sunspot max.

2000.07

202.3

170.1

119.8

2001.12

235.1

132.2

114.6 (-0.9)

2003.03

131.4

61.1

74.0 (-4.3)

2003.04

126.4

60.0

70.1 (-3.9)

2003.05

115.7

55.2

67.6 (-2.5)

2003.06

129.3

77.4

65.0 (-2.6)

2003.07

127.7

83.3

61.8 (-3.2)

2003.08

122.1

72.7

60.0 (-1.8)

2003.09

112.2

48.7

59.5 (-0.5)

2003.10

151.7

65.5

(58.0 predicted, -1.5)

2003.11

140.8

67.3

(55.9 predicted, -2.1)

2003.12

114.9

46.5

(53.3 predicted, -2.6)

2004.01

114.1

37.2

(49.1 predicted, -4.2)

2004.02

107.0

46.0

(44.5 predicted, -4.6)

2004.03

112.0

48.9

(41.7 predicted, -2.8)

2004.04

99.3 (1)

23.6 (2)

(39.6 predicted, -2.1)

1) Running average based on the daily 20:00 UTC observed solar flux value at 2800 MHz.
2) Unofficial, accumulated value based on the Boulder (NOAA/SEC) sunspot number. The official international sunspot number is typically
30-50% less.

This report has been prepared by Jan
Alvestad. It is based partly on my own observations and analysis, and
partly on data from some of these solar data sources. All time references are to the UTC day. Comments and suggestions are always welcome.